conical scanning

A radar scan pattern in which a point on the radar beam describes a circle at the base of a cone. This type of scan pattern provides both elevation and azimuth data. The radiation pattern of the antenna is made slightly lopsided, and the antenna is electrically or mechanically rotated, so that the lobe of maximum radiation rotates about the boresight of the radar dish. When the target is exactly aligned with the boresight, the returned signal is constant in amplitude. This is because the target is always the same angular distance from the lobe of maximum radiation. When the target is not aligned with the boresight, the returned signal is modulated at the frequency of the antenna rotation. In this way, the antenna can be accurately pointed in the direction of the target. The conical scanning method is very precise. This type of scanning is used in some air-interception and fire control radars.

At A, the target is always the same angular distance from the direction of maximum radiation. At B, the target is at varying angles from the direction of maximum radiation. As the antenna is rotated, the signal from the target at A stays constant in amplitude, while that at B fluctuates. This allows precise determination of the target position.